(a) Technical Field
The present invention relates to a semiconductor oxide ink composition for inkjet printing, a method of manufacturing the same, and a method of manufacturing a photoelectric conversion element using the same. In particular, the present invention relates to a semiconductor oxide ink composition appropriate for inkjet printing which helps to effectively produce a photoelectric conversion element, such as a curved dye-sensitized solar cell, a method of manufacturing the semiconductor oxide ink composition, and a method of manufacturing a photoelectric conversion element using the semiconductor oxide ink composition.
(b) Background Art
Recently, the growing interest in environmentally friendly energy has led to intensive research on photoelectric conversion elements such as solar cells. Among them, dye-sensitized solar cells are known to be suitable for building integrated photovoltaics (BIPV) because they can be installed along the curvaceous surface of a building while retaining their visual advantages such as beautiful color tones and translucent characteristics.
Many high-efficiency hybrid electric vehicles (“HEVs”) are provided with a sunroof with a silicon solar cell panel on the top. However, this type of sunroof is opaque and, thus, loses its originally intended attractiveness of openness. Accordingly, there has been a need for the development of sunroofs for vehicles having dye-sensitized solar cells which possess both transparency and an aerodynamically curved design.
A basic structure of a dye-sensitized solar cell includes a working electrode and a counter electrode joined to the working electrode. Dye, a semiconductor oxide, and an electrolyte are injected in between the working electrode and the counter electrode. The dye absorbs light to emit electrons. The semiconductor oxide has porous nano-particles which transport the emitted electrons to an external electrode. The electrolyte releases electrons to make up for the emitted electrons. The oxidized electrolyte may be reduced by the counter electrode.
A basic method of manufacturing a dye-sensitized solar cell will be descried with reference to FIG. 1.
First, a conductive substrate coated with a transparent electrode (transparent conductive layer), such as ITO (Indium doped Tin Oxide) or FTO (Fluorine doped Tin Oxide), which is used as a working electrode, is washed (ST1).
A semiconductor oxide electrode made of TiO2, ZnO, SnO2, or Nb2O5 is then coated on the washed conductive substrate using a screen printing method (ST2), and is subsequently dried and sintered (ST3). In general, a dye-sensitized solar cell exhibits an excellent efficiency when employing TiO2 nano-particles. The coating and sintering are repeated until a desired thickness is achieved.
In the case of a large-area dye sensitized solar cell, a silver grid may be used to raise efficiency (ST4). This step is generally not carried out for a unit cell sized dye sensitized solar cell. Like the semiconductor oxide electrode, the silver grid is subjected to screen printing, drying, and sintering (ST5). The thus treated silver grid is then soaked in a dye for a suitable period of time (for example, for about 24 hrs) so that the dye may be adsorbed thereon, thereby completing the working electrode (ST6).
Next, a conductive substrate coated with a transparent electrode, which is used as a counter electrode, is washed. Platinum is coated on the washed conductive substrate (ST7), followed by drying and sintering (ST8). As described above in connection with the working electrode, a silver grid may be included for a large-area dye-sensitized solar cell to raise efficiency.
The thus manufactured two electrodes (working electrode and counter electrode) are joined together by an organic or inorganic material having adhesive characteristics, such as Surlyn™, epoxy, or glass frit (ST9). An electrolyte is further injected between the two electrodes, thus completing the formation of the dye-sensitized solar cell (ST10).
In the manufacturing process, the sintering steps may be performed at a suitable temperature, for example at a temperature of 400° C. to 800° C., for a suitable time, for example for 5 min to 2 hrs, or longer.
As described above, a general dye-sensitized solar cell is produced by coating various constitutional materials on a planar substrate via a screen printing method.
In order to prepare a desired pattern on a conductive substrate using a screen printing method, a paste is pressingly pushed into the openings of a screen with a dense mesh made of plastic or metal fiber. The substrate, is brought into contact with the openings of the screen, and a predetermined pressure is applied by a squeegee to form a coating layer on the substrate. In performing the screen printing method, it is essential to repeat the drying and sintering processes on a coating layer at least 3-6 times to prevent any damage that might occur during the subsequent screen printing step. As a result, the manufacturing process becomes more complex and the production cost increases.
Moreover, if the dye-sensitized solar cell is manufactured using a curved substrate in the screen printing method, it may lead to a difference in thickness of the coating layer along the substrate surface, such as between the central portion and both ends of the substrate. Further, if the coating process is performed at an increased squeegee pressure in an attempt to prevent such a thickness difference, the mesh may become damaged when fixed under a constant tension. Accordingly, it is difficult to apply the screen printing method to a curved substrate.
Thus, it is necessary to use other processes to manufacture a curved dye-sensitized solar cell, such as a curved dye-sensitized solar cell with two different curvatures of R1 and R2.
In recent years, as technologies for LCDs or OLEDs have been developed, an inkjet printing method used for manufacturing displays or semiconductors has been receiving increased attention because the inkjet printing method is a contactless coating method, and is capable of performing swift coating on a complicated pattern.
However, the inkjet printing method may not be employed for a process of forming a layer with thickness 1 μm or larger, such as a semiconductor oxide layer used for a dye-sensitized solar cell. To apply the inkjet printing method for the formation of a layer having a thickness of 1 μm or higher, it is essential to develop a suitable semiconductor oxide ink composition.
Further, there is no common process to manufacture a dye-sensitized solar cell using the inkjet printing method. Therefore, there is a need for the development of an ink composition capable of forming a semiconductor oxide layer for a dye-sensitized solar cell, and a method of manufacturing a dye-sensitized solar cell using the inkjet printing method.